Average flow between ∼70 RE and ∼220 RE in the geomagnetic tail

Abstract

The ISEE‐3 spacecraft was transferred in 1982 into the magnetotail, where it was kept for about 1 year via succesive lunar swingbys. The Max‐Planck‐Institut/University of Maryland sensor on ISEE‐3 provides energetic ion measurements above ∼30 keV/charge. Assuming that the energetic protons are convected with the local plasma flow we are able to determine the convection velocity from the measured angular distributions and the differential spectrum. A statistical analysis of the flow magnitude and direction at various distance ranges reveals the following: The average tailward flow velocity between 203 and 220 RE is 567 km/s and earthward flow occurs in less than 1% of all cases. At a radial distance of 117 to 153 RE the result is similar; the average tailward flow velocity is found to be 665 km/s and earthward flow occurs in less than 6% of all measurements. This is in contrast to findings at radial distances of 61 to 76 RE. Here, equal probability for earthward and tailward flow has been found and average flow velocities are 336 km/s in both directions. These results indicate that magnetic neutral lines rarely move or form beyond ∼100 RE.